The most recent release of City Navigator Europe includes detailed coverage for the Czech Republic.
There are Garmin authorized companies (independent operators, but authorized by Garmin) that sell vector cartography in Garmin format for some Eastern European countries - for example, Croatia, Poland, et al. I have never used this data, so I can't comment on it. It is fairly expensive on a per-capita basis. You can get more information about this by going to the Garmin website.
My guess, though, is that these companies target their products more at residents of their country than at visitors.
Michael